The present invention relates to containers for carrying and transporting volatile liquids. In particular, the invention relates to a portable container which is particularly suitable for transporting flammable liquids and fuels, such as gasoline.
Flammable liquids, such as gasoline, are often carried in portable containers. By way of example, bush pilots often find it is necessary to carry more fuel than their aircraft can carry in their standard wing tanks, so that after landing in the bush or in a remote location where fuel is not available, they can replenish the fuel tanks of their aircraft. Fuel is also commonly carried in portable containers for use with off-road vehicles and for use by automobile racing teams. Home owners often use portable fuel containers to hold fuel for household devices such as lawn mowers, snow blowers, and for gardening and landscaping equipment. A problem with fueling equipment or vehicles with a volatile, flammable fuel, such as gasoline, is that gasoline vapors are highly flammable, and they are subject to exploding. When gasoline vapors mix with air, an extremely volatile mixture is formed. A spark can ignite this mixture, resulting in an explosive reaction and a fire.
Gasoline is generally carried in either metal or plastic containers. Because metal containers are conductive, they do not build up static charges, as do non-conductive plastic containers of the type heretofore known and used. Also, when metal containers touch the metal fuel filler of an aircraft, either directly, or by using a "grounding strap" of the type used when fuel trucks are used to refuel aircraft, preferably before the container is opened, i.e., before any vapors can form, the potential for a static discharge spark is eliminated. Plastic fuel tanks, of the type heretofore known, have not been made of electrically conductive material, so a static discharge could readily build up on such containers, particularly when used in the cold, dry climates of places like Alaska, where static charges build up easily, but cannot readily find a path to ground. Simply pouring fuel from a container causes a static buildup, which can result in a spark from a static electricity discharge. Alternatively, when it rains, particularly during light rains and drizzles, the rain drops carry an electric charge. If an aircraft is out in the rain its airframe will become charged, and if an attempt is made to fueled it while it is so charged, there is a possibility that a static discharge will occur, resulting in an explosion.
While one would think that the possibility of a fire would be a deterrent to the use of plastic fuel containers, for a number of other reasons plastic containers are preferred over metal containers. Among those reasons are that plastic containers are typically lighter in weight than similar sized metal containers, plastic containers can be molded into arbitrary shapes, plastic containers do not rust, and plastic containers do not dent, scratch, or scratch other items with which they come into contact. In fact, plastic containers are generally preferred, except where they have been banned due to the danger which they impose, e.g, on a number of automotive race tracks.
In order to avoid a fire during a fueling operation, sparks must be avoided, as fuel vapors are inevitably present, and they are invisible, making it difficult to determine their presence. By using a metal gas can, which is electrically connected to the equipment or vehicle, one can assure that the fuel tank and the equipment or vehicle being fueled are at the same electrical potential, thereby minimizing, or eliminating the risk of sparks due to static discharge. However, due to the aforementioned undesirable characteristics of metal fuel containers, e.g., they are prone to denting and rusting, they are heavy, and they are not easily produced in arbitrary shapes, plastic fuel containers are generally preferred over metal fuel containers. Plastic is not typically as strong as metal, nor is it generally conductive. Thus, while plastic fuel containers have been designed, and while they are readily available, the standard plastic filled containers which one can readily purchase are not conductive, so they cannot include means for electrically connecting them to the equipment or vehicle during a fueling operation in order to prevent a static discharge which can potentially ignite the fuel-air vapor which is inevitably present causing an explosion.
In view of the foregoing, it would be desirable to have a conductive fuel container which includes means for providing electrical connection to a vehicle or other piece of equipment which was being fueled so as to provide all of the desirable attributes of a plastic fuel container while still providing a means for electrically attaching the container to the equipment being refueled, whereby there will be no potential difference between the fuel container and the equipment.
Unfortunately, traditional methods for achieving conductive plastics have been unsatisfactory. In particular, either high levels of carbon black have been incorporated via dry blending or melt compounding, or anti-static additives have been used. It has been found that high levels of carbon black severely reduce the properties of the base resin into which they are incorporated, high levels of carbon black severely affect the resin, resulting in poor melt flow characteristics and poor mold fill, and the performance of anti-static additives has been found to degrade over time, as the anti-static additives bleed through the polymer.
Prior attempts to form a conductive plastic fuel container have been made, typically by blow molding processes, but those containers were found to have had walls which were too thin, or too brittle, or too soft, or which did contained air bubbles. Accordingly, these prior efforts failed to provide a conductive plastic fuel container which is strong enough to pass the U.S. Department of Transportation's "drop test".